Until now, the narrowband (hereinafter referred to as “NB” as appropriate) module supported, for example, four wavelengths out of the wavelengths (defined at 50 GHz spacing in each of the C band and the L band) recommended by the International Telecommunication Union (ITU). Therefore, when 40 wavelengths were to be handled by a single transmission apparatus, for instance, it was necessary to prepare ten kinds of NB optical modules (10 kinds×4 wavelengths=40 wavelengths).
In other words, such a demand was met by structuring a wavelength division multiplexing (WDM) transmission apparatus equipped with ten transponders which carry ten kinds of NB modules capable of outputting mutually different wavelengths. In recent years, however, the NB optical module equipped with a full-band tunable laser (hereinafter referred to as FBTL as appropriate) capable of supporting all the wavelengths to be handled by the transmission apparatus (hereinafter referred to as FBTL optical module as appropriate) has been developed, and thus the use of the conventional NB optical module responding to four wavelengths only is coming to an end.
Also, a problem with the 4-wavelength NB optical module has been that, despite a long time it takes to supply it (several months, for instance), the manufacture of it cannot be arranged until instructions on a specific wavelength range to be used are received from a client (until the order for definite wavelengths).
In this regard, the FBTL optical module allows ex-post tuning to all the wavelength bands which the transmission apparatus is supposed to use even when specific information on the wavelength bands is not available in advance. Therefore, the FBTL optical module has its merit in that the arrangement for supply can be started on the information of the required quantity of the module only.
For the existing wavelength division multiplexing (WDM) transmission apparatuses, software for controlling a transponder having a 4-wavelength NB optical module is already in operation with much accumulated control know-how. Even when such a transponder begins to carry the FBTL optical module, there is a practical limitation that no change in the monitoring control unit (typically the control program software for the monitoring control unit) is desired in view of maintaining compatibility with the current wavelength division multiplexing transmission apparatuses already on the market.
Thus, it is desired that even for the wavelength division multiplexing transmission apparatus carrying an FBTL optical module, the monitoring control unit thereof can perform control of the FBTL optical module by the same operation control as one for the conventional NB optical module with four wavelengths assigned.
Non-patent-related Document
    (1) Yoshiharu Fujisaku, et al., “10 Gbit/s Full-Band Tunable Optical Transponder”, Fujikura Technical Journal No. 111, pp. 16-19, October, 2006.